1. Field of the Invention
The present invention relates generally to a testing apparatus for testing performance of a vehicular component associated with an automotive internal combustion engine, such as a power transmission, a transaxle, a differential gear assembly, and so forth. More specifically, the invention relates to a testing apparatus which employs a high inertia power plant, such as an electric motor, a hydrostatic motor, and so forth.
2. Description of the Background Art
Japanese Patent First (unexamined) Publications (Tokkai) Showa 58-38833 and 61-53541 disclose bench testing systems for automatic power transmission. In the disclosed systems, an electric motor, a hydrostatic motor, and so forth, are employed as substitute power plants in place of an automotive internal combustion engine. As can be appreciated, because of a much higher inertia of the electric motor, hydrostatic motor and other substitute power plants in comparison with the automotive internal combustion engines, the substitute power plant is combined with speed increasing devices. Such automotive engine simulation system is useful for a durability test, a static characteristics test and so forth. However, due to a substantially high inertia moment, it is practically difficult to simulate transition characteristics at transmission speed ratio shifting and so forth. For instance, the electric motor has approximately a 10 times higher inertia magnitude than that of the automotive engine.
For designing automatic power transmissions with enhanced shift feeling, a reduced shift shock and so forth, it is essential to obtain data of transition characteristics of a power plant to be actually combined.
Therefore, Tokkai Showa 61-53541 as identified above, employs a strategy of correction of command current for the electric motor. With the corrected command current, the output torque of the electric motor becomes substantially corresponding to the engine output torque to be output in response to a torque demand. Such approach is generally successful in avoiding an influence of high inertia of the high inertia power plant.
However, due to a much higher inertia of the substitute power plant, such as the electric motor, hydrostatic motor, and so forth substituting for the automotive internal combustion engine than that of the engine, the prior proposed simulation systems are not satisfactory as far as simulation of a engine transition state is concerned. For improving this, co-pending U.S. patent application Ser. Nos. 07/427,031, filed on Oct. 25, 1989, and 436,298 filed on Nov. 13, 1989, now U.S. Pat. No. 4,984,988, issued on Jan. 15, 1991, both of which have been assigned to the common owner of the present invention, propose an engine characteristics simulation system for use in a bench testing apparatus for an automatic power transmission. In the prior proposed system, the engine substituting power plant, such as the electric motor, is combined with a speed increasing device for compensating a high inertia of the electric motor and thereby achieving engine equivalent response characteristics with variation of the output torque.
The simulation system disclosed in the above-identified co-pending U.S. patent applications are successful in general in simulating not only the engine steady state but also an engine transition state. However, in case of the actual automotive internal combustion engine, a transmission shift feeling can be affected by various additional factors. For instance, an active state and an inactive state of a dashpot will cause a fluctuation of the engine output torque and thereby cause a variation of the output of the automatic power transmission. Similarly, the presence and absence of an idle-up condition may cause a variation of an auxiliary air flow through an auxiliary air passage to cause a variation of the engine output. As can be appreciated, in order to perform a precise simulation of an engine activity, it is required to control operation of the power plant depending upon factors affecting engine output.